Are any chemists out there that can explain how sterling silver can
contaminate rhodium plate solution? Any suggestions on how to reclaim
the rhodium from the solution? I know I can try to filter the plate
solution with activated charcoal, but can I drop the rhodium out of
the solution completely?

I can’t advise you on refining the rhodium solution - I’ve tried it
with activated charcoal myself, but could never filter it well
enough. But I can empathise with the silver issue - I’ve had it
happen to me, too. What I found was that the silver wires I was
using for contacts were going black and green, and this was gradually
contaminating the solution. To avoid this happening, I started usingfine silver wires, and the problem stopped immediately. If you’re
trying to plate silver items, then my experience suggests a few
things you could try:

Oxidise the items, then pickle them, then barrel them - this will
effectively cover the items with a thin layer of fine silver, but
there may be patches that aren’t covered. Also, it wouldn’t work for
items that need a proper polish.

Silver plate the items first, then rhodium them. I only do
rhodium and gilding - are there any experts that know if silver
plating will work?